The invention pertains to a rotatable cutting tool that is useful for the impingement of earth strata such as, for example, asphaltic roadway material, coal deposits, mineral formations and the like. More specifically, the present invention pertains to a rotatable cutting tool that is useful for the impingement of earth strata wherein the cutting tool body possesses improved strength and design so as to provide for improved performance characteristics for the entire rotatable cutting tool.
Heretofore, rotatable cutting tools have been used to impinge earth strata such as, for example, asphaltic roadway material. Generally speaking, these kinds of rotatable cutting tools have an elongate cutting tool body typically made from steel and a hard tip (or insert) affixed to the cutting tool body at the axial forward end thereof. The hard tip is typically made from a hard material such as, for example, cemented (cobalt) tungsten carbide. The rotatable cutting tool is rotatably retained or held in the bore of a tool holder or, in the alternative, in the bore of a sleeve that is in turn held in the bore of a holder.
The holder is affixed to a driven member such as, for example, a driven drum of a road planing machine. In some designs, the driven member (e.g., drum) carries hundreds of holders wherein each holder carries a rotatable cutting tool. Hence, the driven member may carry hundreds of rotatable cutting tools. The driven member is driven (e.g., rotated) in such a fashion so that the hard tip of each one of the rotatable cutting tools impinges or impacts the earth strata (e.g., asphaltic roadway material) thereby fracturing and breaking up the material into debris.
Especially in a road planning operation in which the rotatable cutting tools impinge an asphaltic kind of material, the so-called breakout angle (or which is sometimes referred to as a fracture angle) is smaller in comparison to other kinds of more brittle material such as, for example coal. In this regard, one can define the breakout angle as the included angle between the central longitudinal axis of the rotatable cutting tool and a plane that generally lies on the fracture surface of the chip or fragment.
When impinging materials like asphaltic material in which there is a smaller breakout angle, there occurs an increase in the extent of contact between the rotatable cutting tool, and in particular the cutting tool body, and the asphaltic material. There are at least two occurrences that result from this increase in side contact.
One such occurrence is that this increase in contact creates more resistance to the movement of the rotatable cutting tool through the asphaltic material so as to thereby require an increase in the horsepower of the driven drum. Although one can increase the horsepower of a driven drum, such an increase adds to the cost of the machine itself, as well as to the cost to operate the road planing machine. It thus becomes apparent that it would be very desirable to provide an improved rotatable cutting tool that can be used for the impingement of earth strata wherein an increase in the horsepower of the driven drum is not necessary to satisfactorily operate for the impingement of material in which there is a smaller breakout angle. Along this same line, it would be desirable to provide an improved rotatable cutting tool that is of such a design so as to reduce the degree of resistance experienced by a rotatable cutting tool in impinging earth strata, and especially for a rotatable cutting tool when it impinges materials like asphaltic material, halite, gypsum, potash or trona in which there is a smaller breakout angle.
Another such occurrence is that this increase in contact creates more abrasive wear of the rotatable cutting tool and especially abrasive wear of the steel cutting tool body. The location of this wear on the steel cutting tool can sometimes be near the axial forward end thereof so as to jeopardize the integrity of the braze joint between the hard tip and the steel cutting tool body. The premature failure of the braze joint between the hard tip and the tool body typically leads to the loss of the hard tip which effectively ends the useful life of the rotatable cutting tool. The loss of the hard tip also typically results in a decrease in the overall operational efficiency of the road planing machine.
It thus becomes apparent that it would be very desirable to provide an improved rotatable cutting tool that has a cutting tool body of such a design so as to reduce the extent of abrasive wear of the cutting tool body during operation, and especially reduce the extent of abrasive wear of the cutting tool body when impinging materials like asphaltic materials that exhibit a smaller breakout angle. It also becomes apparent that it would be very desirable to provide an improved rotatable cutting tool that has a cutting tool body of such a design so as to improve or increase the protection of the braze joint between the hard tip and the cutting tool body during operation, and especially to improve or increase the protection of the braze joint between the hard tip and the cutting tool body when impinging materials like asphaltic materials that exhibit a smaller breakout angle.
In addition to the abrasive wear experienced by a rotatable cutting tool (and especially the cutting tool body) during a road planing application (or other applications in which the rotatable cutting tool impinges earth strata), there is a considerable amount of stress exerted on the rotatable cutting tool including the cutting tool body. If the cutting tool body does not exhibit sufficient strength then there is the risk that the cutting tool body may prematurely fail. Such a premature failure of the cutting tool body is an undesirable result that typically leads to the termination of the useful life of the rotatable cutting tool and a decrease in the operational efficiency of the machine such as a road planing machine. It would thus be very desirable to provide an improved rotatable cutting tool that has a cutting tool body of improved strength so as to reduce the potential for premature failure of the cutting tool body.